In cellular networks, allocation of radio resources to a certain user equipment (UE), also referred to as scheduling, is typically accomplished dynamically on the network side. In the downlink (DL) direction from the cellular network to the UE, a network node may allocate radio resources in accordance with a need to transmit DL data to the UE. The network node may then inform the UE about the allocated resources by sending a DL assignment. For the uplink (UL) direction from the UE to the cellular network, a scheduling request which is sent by the UE to the cellular network may be used to indicate that the UE needs radio resources for sending UL data. An exemplary scenario based on the LTE (Long Term Evolution) radio access technology specified by 3GPP (3rd Generation Partnership Project) is illustrated in FIG. 1. To provide fast scheduling, a base station of the LTE radio access technology, referred to as “evolved Node B” (eNB) is responsible for the scheduling. This may be accomplished dynamically, taking into account the instantaneous traffic pattern and radio propagation characteristics of each UE.
As illustrated in FIG. 1, a UE 10 which needs to send UL data may first send a scheduling request 101 to an eNB 20 which serves the cell of the UE 10. The scheduling request 101 may be sent on a UL control channel, referred to as PUCCH (Physical Uplink Control Channel), providing dedicated resources for sending scheduling requests by the UE 10. These dedicated resources are provided with a certain time periodicity, e.g., every 10 ms. Alternatively, the scheduling request 101 may be sent on a contention based random access channel (RACH). At step 102, the eNB 20 allocates UL radio resources to the UE 10. The amount of allocated resources may vary from between different scheduling transactions. The allocated UL radio resources are indicated in an UL grant 103, which is sent from the eNB 20 to the UE 10. Using the allocated UL radio resources, the UE 10 may then send the UL data 104 to the eNB 20. In addition, the UE 10 may also send a buffer status report (BSR) indicating the amount of buffered UL data to be sent by the UE 10.
In the above process of transmitting the UL data 104, latency occurs which is due to the sending of the scheduling request 101 before the UE 10 can proceed with the transmission of the UL data 104. However, such delay is not desirable in many cases. For example, certain data traffic may be sensitive to latency, such as data traffic associated with online gaming.
The latency problem associated with the sending of scheduling requests can be illustrated by the following example: When the UE 10 has been assigned dedicated resources for sending scheduling requests this means that the UE 10 has a periodic opportunity to send a scheduling request. In the present example a periodicity of 10 ms is assumed. In the worst case scenario, data arrives in an UL transmission buffer of the UE 10 just after an opportunity of sending a scheduling request. Accordingly, the UE 10 will have to wait almost 10 ms for the next opportunity to send a scheduling request. The eNB 20 will respond to the scheduling request with a UL grant, which takes another 2 ms. Accordingly, the delay between data in the UL transmission buffer and the possibility to send the data is at least 12 ms, which may be too long for certain applications.
A known way to address the latency problem is to use periodic pre-scheduling as for example described in WO 2013/085441 A1. In this case, the eNB periodically send UL grants to the UE, without a preceding scheduling request. By the periodic pre-scheduling, a reduced scheduling delay can be achieved, however at the cost of increased resource consumption because resource may be allocated to the UE which are actually not required and the UE needs to respond to each UL grant. Accordingly, it is desirable to utilize the periodic pre-scheduling in the most efficient way.
Accordingly, there is a need for techniques which allow for efficiently controlling radio transmissions in a cellular network, in particular with respect to the scheduling of UL transmissions by periodically sending UL grants.